Prior aerial lifts or hydraulic platforms may include those which are simply telescopic, i.e. a hydraulic cylinder is attached to a pivoted boom to elevate and lower, while one or more extensible booms, the innermost of which carries a workman's cage or basket, may extend from within the pivoted boom. Such types of lifts may be represented by U.S. Pat. No. 3,056,510 and by the Versalift lift, manufactured by Time Manufacturing Company of Waxco, Tex. Another type of lift may include a pair of booms, with the inner end of the upper boom pivotally connected to the outer end of the lower boom. The lower boom is elevated and lowered by a hydraulic cylinder, while the upper boom is elevated and lowered by a second hydraulic cylinder, pivotally connected between the booms. This type of lift may be represented by U.S. Pat. Nos. 3,670,849 and 4,081,055. In another type, which may be represented by the Dur-a-Lift, supplied by Durnell Manufacturing, Inc. of Emmetsburg, Iowa, a hydraulic cylinder, connecting the lower boom with the upper boom, is articulated by a linkage system which is connected to the upper boom and lower boom, as at points spaced from a pivotal connection between the two booms. A similar construction is shown by U.S. Pat. No. 4,222,457. There are also combination articulated and telescopic types of lifts, such as the Condor supplied by Calavar Corporation of Santa Fe Springs, Calif. in which both the lower boom and the upper boom are provided with an extensible boom, with the inner end of the upper boom pivoted on the outer end of the lower extensible boom and an articulating linkage connecting the two. As a result, the workman's basket can be raised to a considerable height, such as to a distance on the order of 144 feet from the ground. In another type, the articulation is inverted by rods or cables connected through levers, with the raising and lowering controlled by hydraulic cylinders of larger diameter but relatively short stroke. One example of this type if the Stel-Lift, produced by Stelco, Inc., of Overland Park, Kans. In other types, the telescopic effect is limited by mechanical construction, such as a ladder which is pivoted upwardly and extended by cables, as in the case of the aerial ladder manufactured by Van Ladder, Inc. of Spencer, Iowa.
One of the problems associated with any aerial lift, which is to be extended in any direction except fore and aft of the vehicle carrying it, is the problem of balance of the vehicle at higher positions of the basket, particularly lateral extensions. Since the lateral distance between wheels of a vehicle is normally considerably less than the length of its wheel base, the problem of imbalance becomes more acute as the lift is rotated to a lateral position, i.e. at 90.degree. to the longitudinal axis of the vehicle. The customary manner, in which such a problem has been overcome, is by the use of jacklegs or outriggers of various types, such as those which engage the ground at a point beneath the lateral edge of the vehicle; others are extended laterally for a distance by being pivoted downwardly and outwardly, while a similar result may be accomplished by use of a linkage system. There also are types of outriggers which include a moveable beam which is extended laterally from the vehicle for a considerable distance, then a leg is pivoted, or moved downwardly from the beam, in order to engage the ground. Generally speaking, outriggers or jacklegs require considerable time for setup and increase considerably the cost of the complete vehicle and aerial lift.
Among the objects of this invention are to provide an aerial lift which normally does not require outriggers, jacklegs or similar types of support for a vehicle; to provide such an aerial lift which permits rotation during use through a full 360.degree. at any position; to provide such a lift which is inherently balanced by its construction; to provide such a lift which will accommodate extension and retraction of an extensible boom in addition to conventional lower and upper booms; to provide such a lift which requires a single hydraulic cylinder only, to raise and lower a pair of pivotally connected, lower and upper booms; to provide such a lift having a workman's basket which is inherently moveable to any position in a desirable work area; to provide such a lift which causes the workman's basket to move generally upwardly when the hydraulic cylinder is extended, rather than in an arc toward or away from the vehicle; to provide such an aerial lift which may be made so that it does not require connection of controls or hydraulic hoses to the vehicle; to provide such an aerial lift which may be completely controlled from a workman's basket; to provide a supply line for a nozzle at the upper end of the lift, which will accommodate relative movement between various parts of the lift, as well as rotation of the lift to different angular positions; to provide such a lift which may be easily locked in a storage position to minimize bearing stresses due to sway of lift parts during movement of the vehicle along a road or the like, as well as unlocked when use of the lift is to be resumed; and to provide such a lift which is effective in operation and relatively low in cost.